This invention relates to catalytic hydrohalogenation processes. In particular, the invention relates to the catalytic hydrohalogenation of hydrocarbyl compounds, such as methanol, to produce hydrocarbyl halides, such as methyl chloride.
Chlorinated hydrocarbons have various utilities as industrial chemicals and solvents. For example, methyl chloride is useful as a catalyst carrier in low temperature polymerization; as a fluid for thermometric and thermostatic equipment; as a methylating agent in organic synthesis, such as the synthesis of methylcellulose; in the preparation of silicone rubbers; and as an extractant and low temperature solvent.
Methods for the production of halogenated, especially chlorinated, hydrocarbons, such as methyl chloride, are well-known. In a typical method for the production of methyl chloride, vaporized methanol and hydrogen chloride are mixed in approximately equimolar proportions and passed through a converter packed with a catalyst such as alumina gel or zinc chloride on activated carbon to form methyl chloride. Other known methods involve reactions in the liquid phase using an aqueous solution of catalyst. For example, U.S. Pat. No. 4,073,816 teaches that monochloroalkanes or monochlorocycloalkanes can be prepared by reacting an alcohol with hydrogen chloride in the presence of aqueous zinc chloride. German Offentlegungschrift 3332253 teaches that mixtures containing alcohols and ethers may be converted to alkyl halides by reactions with hydrogen chloride in the gas phase in the presence of an zinc chloride on aluminum oxide catalyst. This reference further teaches that small amounts of alkali metal chlorides and larger amounts of cadmium, iron and/or magnesium chlorides may be added with the zinc chloride to increase the efficiency of the catalyst.
Such methods do not resolve all the existing problems relating to the manufacture of chlorinated hydrocarbons. The problems include excessive production of byproducts; requirements for use of excess hydrochloric acid and excessive coking of the catalyst. An additional problem related to the use of alumina or alumina supported catalysts is the chemical breakdown of the alumina to produce other less desirable types of alumina such as boehmite, a monohydrate of alpha-alumina, and also physical attrition. What is needed is a catalyst which results in a high yield of chlorinated hydrocarbyl compound which also permits the complete conversion of hydrochloric acid; which does not experience excessive coke formation; which reduces the amount of byproducts formed; which decreases the formation of boehmite; and which is more resistant to attrition.